This invention pertains to a new binder composition suitable for use in bonding a particulate material such as sand or other refractory or foundry material to make a shaped article.
It is known in the art to employ phenol-formaldehyde resole resins to bond granular refractory material, e.g., in a foundry molding composition. For example, U.S. Pat. No. 4,426,467 to Quist et al. discloses such a composition which is curable at room temperature using a lactone as curing agent. While such compositions are extremely desirable inasmuch as they are curable at ambient temperature, such resins may have unacceptable thermal properties, i.e., they may experience veining and tearing at high temperatures experienced when subjected to molten metal in the foundry. Such resins are also especially deficient for use in preparing refractory articles, which, in addition to being able to withstand extremely high temperatures (e.g., for use in furnaces), must optimally contribute carbon when sintered. The carbon contributes to the dimensional stability of the articles via refractory bonding (i.e., through durable carbon-carbon bonds and carbon-aggregate bonds) and also provides abrasion resistance.
To obviate these problems of thermal insufficiency and insufficient provision of residual carbon, phenolic novolak resins may be tried. However, these novolak resins are undesirable inasmuch as they require heat to cure, resulting in numerous problems, among the most significant of which are (1) the evolution of noxious formaldehyde fumes which result from heating phenol formaldehyde resins, and (2) practically no "green strength", or room temperature cure.
It is also known to use a phenol-formaldehyde novolak resin to bond a carbonaceous aggregate, such as is disclosed in Chandramouli et al., U.S. Ser. No. 848,468, filed Apr. 7, 1986 now U.S. Pat. No. 4,775,455 (assigned to the assignee of the present invention). In a preferred teaching therein, a blend of a novolak and a resole resin, both phenol-formaldehyde resins, may be employed, but require thermal curing, or high acid levels. A need exists for a binder able to provide adequate green strength by a room temperature cure, and which also provides high strength after heat treatment.